Automatic circuit tuning



:electron dischargedevice. Y

Patented Sept. 19, 1944 AUTOMATIC CIRCUIT TUNING Hallan E. Goldstne, Port J eerson, N. Y., assigner to Radio Corporationrof America, a corporav tion of Delaware "Application 29, 1942, Serial No'. 440,899

(ci. 25o-'17) 9 Claims.

The present invention, broadly stated, com` prises an automatic tuning system for assuring the proper phase relationvbetween the input and output voltages of an electronV discharge device.

The invention iS described hereinafter with particular reference to a radio transmitter. In high power radio transmitters,- it is important for the plate tank circuit (oscillatory circuit) of the Vpower amplier to be correctly maintained in resonance. Often, thereis provided a long transmission line which extends from the plate tank circuit of the power amplifier tothe antenna for feeding ,energy to the antenna. If the impedance of the transmission line or antenna changes due to climatic conditions such as raIn, snow, sleet, wind, etc., the loading onfthe transmitter will also change and thiscondition will reflect an impedance upon thetransmitter whichpwill change the tuning of the plate tank circuit of the power amplier Vfrom its .correct value. Suohanunde- Y sired Vchange in the tuning of the power amplifier is, in effect, a change in the phase of the output voltage with -respect tothe input voltagefand -may cause a large, increase in the plate current ofthe amplier withconsequent damage to the The kpresent invention ,v overcomes Vthe foregoing difliculties by providing a system which automatically tunes the tank circuit of the power amplifier, or lof any other desired .vacuum ,tube stage, in order to maintain the phase of the plate 1 voltage at the correct relation to the grid voltage.

In this way I am able toY prevent undesired energy losses in the plate circuit of the tube and maintain the operation of the system at. high eiciency.

AAn important feature ofthe inventionresides in an arrangement which utilizes the same standard oscillator furnishing the basic frequency for the transmitter foroproviding a lower frequency `which serves, in a Waydescribedin more detail later, to energize a motor in order to restore the tuning to its correct value. This arrangement requires the-use of a heterodyne oscillator and enables me to standardize all ofthelow frequency apparatus. A description of` the invention vfollows in conjunction with a drawing whose single figure illustrates an embodiment of the inventiomapplied to a high power lradio transmitter.

Referring-to the drawing, there is. shovvnldia--` grammatically only) a high power radio trans- `mitter comprisinga crystal oscillator I, a frequency multiplier 2, a power amplifier 3' having an input tank circuit 4 and an output tank circuit 5. and a transmission line -TL coupled to the'tank and 2l. Y Transformer 20 is so arranged as to circuit 5 and feeding` energy to a remote antenna c 6. Onlythose'parts of the transmitter have'beetlshown which are essential to an understanding of4 the principles of the invention. Forn purposes of l exposition only, let us assumethat therAcrystal-j'j' oscillator I generates'stable oscillations, 0121000 kilocycles, and that the vrfrequ cyl;multiplierv 2j multiplies the output of the ci ator to 9000 kilocycles. If the output tank circuiti!) is'tuned to resonance (9000 kilocycls'fgthen 'n the plate current of amplifier 3 Will be in'ph'ase with the voltage on the input grid of the amplifier, and the plate voltage kwill be .illirout-of-phase with the grid voltage on the sainetripje'v -cIn orderto assure this phase relationship,tl;iereis providedV an automatic tuning. systemv which will `now be .described. c v l The crystal `frequency of loscillator I is multiplied by frequencymultiplier-lto`8000 kilocycles and oscillations of this 8000 .kilocyclefrequency are supplied to frequency converters or mixersv IlV and 9 whichfreceive over leadsl and: I I, respec-V tively, currents from the input andvoutput tank circuits 4 and 5 of power amplifier 3.- Since the currents in tanks 8 and 9 have a frequency of 9000 kilocycles, therewill be produced in the outputs of these frequency converters currents of a frequency of 1000 kilocycles. A stable-heterodyne oscillator I2. preferably a crystal-controlled type, provides currents which beat with the 1000 kilocycle outputv currents fr ornnconverters yIi and Y 9 in additional frequency converters I3 and I4,'

respectively, toprpduce audio frequencyoutputs in leads I5 and Iii` ofg100 cycles each. One of these cycle currents, here shown as appearing in lead IB, is fed to a Vphase shifter .I1 and then to an audio amplifier I8.V The other 100 'cycle current in lead I5 is fed to an audioV amplifier I9. In the outputs of these audio amplifiers'. I8 and I9 there are provided a pair of transformers 20 produce Ain its output coil 22 a. voltagevwhich iS the vector sum of ,the voltages applied to the audio4 amplifiers, while transformer ZI is soarranged as to produce invitsv output coil `24 (a voltage which isthe vector difference ofthe'voltag'es l applied to the audio amplifiers. Coilsv22 and 24 o are coupled byk means 4of leadsV 2 5"V and 26, re-

spectively, to differentccoils of a small two-phase reversible motor M whose rotatable armatureis linked by a shaft, shown by dashlines ?'I,to a variable reactance (here shown the condenser) in the output ltank circuit Ii.v Motor Mis used 'to tune the power amplier tank, circuit ;5. 'Y

The sum voltage in leadsj isfSO ollfoffphsci ting of the tuning of the output tank 5. If thereV v is any undesired difference in phase between theV input and output voltages derived fromfitarrksfll" and 5, respectively, we can'then compensate. for.

this undesired difference by--means of an `'adj-usti ment in the phase shifter l1.

In the operation of the system, any departure from normal of the phase relation between *the voltages in tanks 4 and 5, due to reflections caused `by climatic conditions affecting the antenna, will produce la movement lin the motor of such sn'sean'd magnitude aS-'to krestore 1the vphase relatin between the voltages the input' and output `tank circuits '4 and Sito normal. fTh radio transmitter :is also shown lsupplied witha" c'ouplingcontrol feature comprising-a plate current i relay '30 in the `catliode circuitV of the Vpcii'reranfipliiienand'a reversible motor Mlin'ked t'the 'transformer *3| "'Relay' works fbet-ween fdesired current Iiiazimum and'icurrent minimum lii'nit's.` This motor M' 1vaines -the coupling l.te- "tweenthei antenna :load-andithetoutput tan-k ciruitto assureconstant'poweroutputifrom power 'amplifier c; 1 'Without this coupling-control :feature, thepo'wer amplierlnayfalways workir'itol a resistive load bec'ause 'ofthe y'einzeln-atie `tuning system but may not work into the optimum Ior 'proper'loaddeterinined byva-rious factors. 'Motor M'iisinte'rlocked' ina'ma-nnernot'shown, tol-invsure: its operation only' aftermotor M-has iluncjO'ne advantageof Athe-presentinvention'lliessin the ease with-whichthellow lfrequency equipment A'canr'be standardized; l This 4in virtue-of the "heterodynel circui-twhichheatsfthei highlfrequen- Aclefsd'okvvn toaudiof'requencziesr f 'l l 1 iihat isc-lainie'dli's': 'Y v r v A 1. The method ofniaiitainingia predetermined `"phase relation -btweenithei waves in-apair `of fcascaded tank lcircuits tnedf'to 'the same lfre- '""queny f'which conpris`es Afderivirig z currents :from f :Teach-'of saidtankecircuits, ibeati-rig fsaid currents with 'stable ifrequency oscillations (tol produce a paix-of lower freduencycurrents -of the same fre- *fquen'cy combining said vlowerfrequency currents Uto 'produce two lphase' displaced -Lv'oltages lone of *which isfequallto-the vectori'sum andthe-other "of which Vis `r-equal-to Ythe vector difference of-the 'j voltages '-produced l-at fsaid Ylower frequency and utilizing said twojpha-'se displaced voltauges-to vary the tuning of one- "of said #tank circuits in that L ldirection r-Which willmaintaiir said-predetermined phase relation.

2,. :The method fof;automatically-maintaining a N"desired Iphase relationl'between the resonancefrequency LofV a tunedj(ircuit and the frequency of 'energyi supplied thertolwhiclr includes lsepV arately mixing-current-derived omisaid tuned-,;circuit fand "current A:from lthef-''en`ergy suppliedfthereto "withoscillations fofa stable frequencylto-produce 3lower lfrequencycu'rrent's,beatingsaid lower `frequencylf currents l'fdown t'o Laudio ifrequency curlrents ofv "the same i frequency, combining L said audio frequency? currents -tciiproduce" two. phasequadrature displaced -ivoltagesi one off-which is equal to the vector sum and the other of which is equal to the vector difference of the voltages of the currents at said audio frequency, and utilizing said two phase displaced voltages to vary the 5 tuning of said tuned circuit in that direction which will maintain said desired phase relation. 3. In a system having an electron discharge device and vgrid input and .plate output tuned circuits tuned to the same-frequency', anarrangement for automatically maintaining a desired 'zphase relation between the input and4 output voltages of said electron discharge device, comprising "fmeans-forseparately beating energy derived from -saidtunedecircuits down to currents of the same audio frequency, an audio amplifier for amplifying each -of Vsaidvaudio frequency currents, and means including a pair of audio transformers in V'the outputcircuits of said amplifiers for obtaining 'two phase displaced voltages one of which is equal to the vector sum andthe other of which "isf equal "to 'the -'-vec't'or diuere'nce "of the voltages I-`applied` tosaid `audio1ain-plifiers,V la kt-wo-iihas'e-re- 'versible motorlcouiiledfto'said transformers, and a mechanical link between theirotatalble element *said tunedcircuits #f or varyingithe ltunin-g i of said one tuned circuit V'in that :direction lwliioh will maintain-said desiredlp'has'e irela'tion.

4. -In -a radioltransniitter having-alpow'er :am- '"plier,!grid input and Ilplatecutiaiut tunedcircuits therefore, and alloadcouple'd to said foutput tuned lcircuit;anarrangement.for maintainingtheioutjput tuned circuit a`t1i-tsiresonance frequency -Ldespite changes-in- `lo'siding.comprising Lconnections extendirrgfdirectly-rrom-lsaidiinput-and' output circuits-toseparate-frequencyconverters,means for supplyingsaid-converters Lwithf stable :oscillations -`to fproduce --in -the #output icircuits ltof." said .con- -verterslcurrents jof the-same fbutio'f a :lower fre- 40"quency -than --tho'se-i-n said' tuned circuitarim'eans -for combining. currentsiiderived fromfsaid ilower frequency to #produce Vtwb-phase' displaced Vvolta-gesfon'e-of which isre'qual toitheivector sumand the -'ether-'of which is-'cqual t01 the 'vectondiffereme) offth'e voltages` of-r said Vci'1rrents,:and an .electromechanical device ce's'ponsive cto said ph-ase displaced voltages for .waiyingcthetuning ofc-.said 7amplifier loutput Ltune'd circuit ,in l:that direction -whichwillmaintain itins resonance. i5. lIn lapradio 'transmitter ihaving arstable .oscillator-furnishing i energnyto arpowersampller, tin- -pu't landoutput Ltuned fcircuitsfor `ssaid .'amplier, :fa-load.includinglanvantennafcoupledLtozsaidsout- `put-tuned circuit, an: arrangement for maintainin'gtlie `output tuned'c-ircuit at:its I*resonance-fre- -quency #despite changes .Ein .floadinjg comprising -eonnections feidaending' idirectly yfrom -said 4input l and Jutput circuits ito `separate frequency con- Ivertersmeans fonsupplyin'gisaidconverters `with @oscillations fderivedifromsaid oscillator for rpro- 'ducingein the -zoutput r,circuits ofisa-id converters currents of the Lsame 'but of :a flower frequency #thanlthosef-in :said tuned circuits, additionallcon- "'-verters fori` separatelyimixing "ther currents of-said lower frequency with additionalo s-:il-Iationsv of a.-1stable .l frequency to ;profduce two currents of -thessame audio frequency,-wa;phase-shifter for one :of said flast ytwo-currents .-forcompensating for any undesired'idierence un fphase between the 70 :voltages derivedfrom` saidsinput iandoutpvuttuned -Icircuitsfand-meansincludingY an electromechanical devicev` responsive tto -V-a changer-in .the Lph'ase fbetween said :last -two currents :for varying the -ftuning' ,of 'said- Aoutputtuned circuit: in that 'direc- 'tion I'Which-will.-maintainfit in..resonance.

6. In a radio transmitter having a stable oscillator furnishing energy to a power amplier, input and output tuned circuits for said amplifier, a load including an antenna coupled to said outpu-t tuned circuit, an arrangement for maintaining the output tuned circuit at its resonance frequency despite changes in loading comprising connections extending directly from said input and output circuits to separate frequency converters, means for supplying said converters with oscillations derived from said oscillator for lproducing in the output circuits of said converters currents of the same but of a lower frequency than those in said tuned circuits, additional converters for separately mixing the currents of said lower frequency with additional oscillations of a. stable frequency to produce two currents of the same audio frequency, a phase shifter for one of said last two currents, means for combining the audio frequency currents to produce two phase displaced voltages in quadrature one of which is equal to the vector sum and the other of which is equal to the vector diierence of the voltages of said audio currents, and an electromechanical device responsive to said phase displaced voltages for varying the tuning of said amplier output tuned circuit in that direction which will maintain it in resonance. i

'1. A system in accordance with claim 5, including a frequency multiplier for said transmitter Yand a frequency multiplier between saidstable oscillator and said rst converters.

1 8. The combination with an electron discharge device having grid input and plate output tuned circuits tuned to the same frequency, of an arrangement for automatically maintaining a desired phase relationrbetween the input and output voltages of said device, comprising means for comparing voltages representative of said input.

vcircuit in that direction which will maintain said desired phase relation.

9. The combination with a vacuum tube ampliiier having input and output tuned circuits, one of which is tunable over a range of frequencies, of any arrangement for automatically maintaining a 180 phase relation between the input and output voltages of said vacuum tube amplifier,

comprising a reversible motor having its rotatable armature linked to said one tuned circuit for tuning the same in such direction as to restore said 180 phase relation, a pair of iield coils for said motor, yand means for comparing voltages representative of said input and output voltages and for applying the resultants to said field coils to produce rotation of said motor whenever there is a departure of said voltages from the relation.

HALLAN E. GOLDSTINE. 

